Method for ammoxidation of paraffins and catalyst system therefor

ABSTRACT

Disclosed is ammoxidation of C 3  to C 5  acyclic alkanes with NH 3  and O 2  using (1) a mole ratio of alkane:NH 3  in the range from 2 to 16 and a mole ratio of alkane:O 2  in the range 1 to 10 and (2) a mixture of particulate catalyst compositions, the first being especially effective to promote formation of an unsaturated nitrile and an olefin from the paraffin, and the second catalyst composition being especially effective to promote the conversion of the olefin to the unsaturated mononitrile. Catalyst compositions useful in the process are also disclosed.

This a division of co-pending application Ser. No. 200,325, pending,filed May 31, 1988

This invention relates to an improved process for the catalyticammoxidation of paraffins containing from 3 to 5 carbon atoms to α,β-unsaturated mononitriles, especially paraffins containing 3 to 4carbon atoms. Most important is the ammoxidation of isobutane tomethacrylonitrile and, especially, of propane to acrylonitrile.

Because of the price differential between propylene and propane aneconomic incentive exists for the development of a viable catalyticprocess for conversion of propane to acrylonitrile.

Earlier attempts in the prior art to develop an efficient process forthe ammoxidation of propane to acrylonitrile produced eitherinsufficient yields or processes that necessitated adding halogenpromoters to the feed. The latter procedure would require not onlyreactors made of special corrosion resistant materials, but also thequantitative recovery of the promoter. The added costs thus eliminatedthe advantage of the propane/propylene price differential.

It is thus an object of the present invention to provide an improvedprocess for the ammoxidation of paraffins to unsaturated mononitriles.

It is a further object of the invention to provide new catalyst systemsfor such process.

Still another object is to provide an improved catalytic ammoxidationprocess for making unsaturated mononitriles from lower paraffins withoutthe use of halogen promoters.

Other objects, as well as aspects, features and advantages, of thepresent invention will become apparent from a study of the accompanyingdisclosure and the claims.

The foregoing and other objects of the present invention are achieved bythe process of the present invention. There are two main features of thepresent process invention. The first of these is the use of an excess ofthe alkane feed with relation to NH₃ and molecular oxygen. The secondfeature, which is used in combination with the high ratio of the C₃ toC₅ paraffin to NH₃ and O₂, is that a combination, i.e., a mixture, ofcatalysts is employed, the first catalyst composition being especiallyeffective to promote formation of an unsaturated mononitrile and anolefin from the paraffin, and the second catalyst composition beingespecially effective to promote the conversion of the olefin to theunsaturated nitrile. Such mixture is the subject of the compositionclaims herein.

In the present application "paraffin" designates an acyclic paraffin.

British patent specifications Nos. 1,336,135 and 1,336,136 disclose theuse of high ratios of propane or isobutane to ammonia and oxygen, butonly single ammoxidation catalysts are used, and the yields ofacrylonitrile are extremely poor. U.S. Pat. No. 3,860,534 also disclosesuse of such high ratios, using a catalyst containing only V and Sboxides. However, after the catalyst is calcined, it is washed for 24hours with water and dried, a laborious procedure. A. N. Shatalova etal, in Neftekhiniya 8, No. 4,609-612 (1968), describe the reaction ofpropane with oxygen and ammonia using a large excess of propane and amixture of two catalysts, one of which is described as oxides of metalshaving dehydrogenating characteristics at 550° and 600° C. At 500° C.little or no acrylonitrile was produced. Rather large amounts ofpropionitrile and acrolein were made per mole of acrylonitrile produced.The per pass conversion of propane to acrylonitrile was generally 2-4percent with selectivity to acrylonitrile being from 12 to 33 percent.

In the present process when applied to propane ammoxidation a smallamount of propylene is produced in relation to the unreacted propane inthe effluent. Such propane effluent containing propylene in the amountof up to 8 mole percent, but usually no more than 6 mole percent, of theamount of propane plus propylene can comprise the substrate feed to thepresent process. And in general the C₃ to C₅ alkane feed to the processcan contain one or more C₃ to C₅ olefins. The C₃ to C₅ olefin content ofthe feed to the present ammoxidation process can contain from zero to 8mole percent of such olefin(s), based on the moles of C₃ to C₅ paraffinplus olefins fed, and this feed can be from any source. Although largeramounts of C₃ to C₅ olefins may be present in the substrate paraffinfeed, usual amounts are as stated, and the usual olefin is thatcorresponding to the particular paraffin fed to the reaction zone of thepresent process.

According to one aspect of the present invention there is provided aprocess for the ammoxidation of a C₃ to C₅ paraffin to an α,β-unsaturated mononitrile which comprises contacting in a reaction zonesaid paraffin in the vapor phase in admixture with ammonia, molecularoxygen, and optionally an inert gaseous diluent, with an intimateparticulate mixture of a first catalyst composition and a secondcatalyst composition, said feed to the reaction zone containing a moleratio of paraffin:NH₃ in the range from 2 to 16 (usually 3-7), and amole ratio of paraffin to O₂ in the range from 1 to 10 (usually 1.5-5),said first catalyst composition being 0-99 weight percent of adiluent/support and 100-1 weight percent of a catalyst having oxygen andthe cation components in the proportions indicated by the empiricalformula:

    Bi.sub.a V.sub.b L.sub.l M.sub.m T.sub.t O.sub.x,          formula (1)

wherein

L is one or more of K, Cs, Rb and Tl;

M is one or more of Mo, W, Cr, Ge, Sb, Sn, P, Pb and B;

T is one or more of Zn, Nb, Ta, Fe, Co, Ni Cu, Mn,

Ti and rare earths;

a=1-25

b=1-50

l=0-1, usually 0-0.2

m=0.1-20

t=0-20

x is determined by the oxidation state of the other elements in thecatalyst,

(a+b):(l+m+t)=20:1 to 1:5

a:b=1:5-5:1, usually 1:3-3:1,

with the proviso that the atomic ratio of Mo:V is zero to <10; saidsecond catalyst composition being 0-99 weight percent of adiluent/support and 100-1 weight percent of a catalyst having oxygen andthe cation components in the proportions indicated by the empiricalformula:

    Bi.sub.n Ce.sub.p D.sub.d E.sub.e F.sub.f Mo.sub.12 W.sub.g V.sub.v O.sub.yformula ( 2)

where

D is one or more of Fe, Mn, Pb, Co, Ni, Cu, Sn, P, Cr, Y, Mg, Ca, Sr, Baand rare earths other than Ce and Sm;

E is one or more of Sb, Ge, As, Se, and Te;

F is one or more of an alkali metal, Tl, Ag and Sm and where

n is 0.01-24, p is 0.01-24; (n+p) is 0.1-24, d is 0-10, e is 0-10, f is0-6, g is 0-8, v is 0-0.5 and y is determined by the oxidation is 0-6, gis 0-8, v is 0-0.5 and y is determined by the oxidation state of theother elements present, wherein the weight ratio in said mixture of saidfirst catalyst composition to said second catalyst composition is in therange of 0.001 to 2.5.

By "particulate mixture" as used herein is meant a mixture of solidparticles or subdivided pieces of the first catalyst composition withseparate and distinct solid particles of the second catalystcomposition. The particles are often of a size used in fluidized bedreactors, say about 40 to 90 microns, but of course larger particles ofcatalyst can be employed for use in fixed or gravity flowing catalystbeds.

"Rare earths" as used herein means atomic numbers 57 through 71.

In the present process in all its embodiments the ratio of O₂ to NH₃ fedto the reaction zone is usually in the range from 1 to 10 (more often1-5) and the ratio of inert gaseous diluent to paraffin is usually inthe range zero to 5 (more often zero to 3).

The diluent or support for either catalyst composition is a refractorymetal oxide or mixture, such as silica, silica-alumina, etc.

In the usual practice of the present invention the catalystsupport/diluent for the catalyst of formula (1) is not an oxide of anelement named in formula (1). Further, in the usual practice of theinvention the catalyst support/diluent for the catalyst of formula (2)is not an oxide of an element named in formula (2).

In the catalyst compositions of the invention the catalyst empiricalformulas (1) and (2) do not, of course, connote any particular chemicalcompound, nor indicate whether the elements are present as a mixture ofindividual oxides or as a complex oxide or oxides, or what separatecrystalline phases or solid solutions may be present. Similarly, thedesignation of certain oxides, such as "silica" or "alumina" or SiO₂ orAl₂ O₃, as supports or diluents is merely in accordance with conventionin the inorganic oxide catalyst art, and such designations refer tocompounds often regarded as supports in the catalyst art. Suchdesignations, however, do not mean that the element involved is actuallypresent as a simple oxide. Indeed, such elements may at times be presentas a complex oxide with one, more than one, or all of the elements informula (1) or formula (2), which complex oxides form during theprecipitation or agglomeration, drying and calcining process forpreparing the catalyst composition.

The process of the invention is especially useful in the ammoxidation ofpropane or isobutane.

In the preparation of the catalyst compositions of formula (1) orformula (2) the metal oxides can be blended together or can be formedseparately and then blended or formed separately or together in situ. Auseful manner of incorporating promoter elements is by choosing awater-soluble salt of the promoter element, forming an aqueous solutionof the salt, and mixing the solution with a solution or a suspension ofthe base elements or salts thereof. Optionally, the promoter elementsmay be incorporated by the use of soluble complex salts or compoundswith the desired base elements which upon calcination will yield thedesired ratio of the elements in the finished catalyst.

Bismuth may be introduced into the catalyst as an oxide or as any saltwhich upon calcination will yield the oxide. Most preferred are thewater-soluble salts which are easily dispersible within the catalyst andwhich form stable oxides upon heat-treating. The most preferred salt forintroducing bismuth is bismuth nitrate.

To introduce the molybdenum component any molybdenum oxide such as thedioxide, trioxide, pentoxide or sesquioxide may be used; more preferredis hydrolyzable or decomposable molybdenum salt such as molybdenumhalide. A preferred starting material is ammonium heptamolybdate.

Other variations in starting materials will suggest themselves to oneskilled in the art, particularly when the preferred starting materialsmentioned hereinabove are unsuited to the economics of large-scalemanufacture. In general, any compounds containing the desired catalystcomponents may be used provided that they result, upon heating to atemperature within the range disclosed hereinafter, in the oxides of theinstant catalyst.

These catalyst compositions can conveniently be prepared by slurrytechniques wherein an aqueous slurry containing all of the elements inthe objective catalyst is produced. In any event, a solution or slurrycontaining all of the elements of the catalyst is formed. This isfollowed by evaporation, drying and then calcining the product in amolecular oxygen-containing atmosphere, such as air, at from 350° to700° or 750° C., usually 400° to 650° C. The length of the calcinationperiod may range from 30 minutes to 12 hours, but satisfactory catalystcompositions are usually obtained by calcination at such temperaturesfor a period of from 1 to 5 hours. Until calcination the compositionsare not catalysts but are merely precatalysts with little or nocatalytic activity. Liquids other than water, such as C₁ to C₈ alcoholscan also be used to form the precatalyst slurry.

In the ammoxidation of the present invention, the reaction is carriedout in the gas phase by contacting a mixture of the paraffin, ammoniaand molecular oxygen, and inert diluent, if any, conveniently in a fixedbed of the catalyst mixture, or a gravity flowing bed, a fluidized bedor a fast transport reactor mode.

Examples of inert diluents useful in the reaction are N₂, He, CO₂, H₂ Oand Ar.

The reaction temperature range can vary from 350° to 700° C., but isusually 430° to 520° C. The latter temperature range is especiallyuseful in the case of propane ammoxidation to acrylonitrile.

The average contact time can often be from 0.01 to 10 seconds, but isusually from 0.02 to 10 seconds, more usually from 0.1 to 5 seconds.

The pressure of the reaction usually ranges from 2 to 45 psia. Mostoften, pressure is somewhat above atmospheric.

The following examples of the invention are exemplary and should not betaken as in any way limiting.

EXAMPLE 1

Bismuth nitrate dissolved in dilute nitric acid was mixed with asolution containing ammonium metavanadate and ammonium heptamolybdatedissolved in hot water. Silica sol and alumina sol were added to thisand the slurry was evaporated to dryness over a hot plate. The drymaterial was heat treated at 290° C. /3 hrs, 425° C./3 hrs and 610° C./3 hrs. The composition of the catalyst was 50% BiV₀.7 Mo₀.5 O_(x) +25%SiO₂ +25% Al₂ O₃.

EXAMPLE 2

A catalyst with the composition 50% BiV₀.7 Mo₀.5 SbO_(x) +25% SiO₂ +25%Al₂ O₃ was prepared as described in Example 1, except that Sb₂ O₅ solwas added to the ammonium metavanadate and ammonium heptamolybdatesolution.

EXAMPLE 3

This catalyst with the composition of 50% BiV₀.7 Mo₀.5 Cr₀.5 O_(x) +25%SiO₂ +25% Al₂ O₃ was prepared as in Example 1 except that chromiumnitrate dissolved in water was added to the bismuth nitrate solution.

EXAMPLE 4

This catalyst with the composition 50% BiV₀.7 Mo₀.5 Cr₀.5 O_(x) +50% Al₂O₃ was prepared as described in Example 3, except that no silica sol wasused.

EXAMPLE 5

A solution containing chromium nitrate and bismuth nitrate dissolved indilute nitric acid was mixed with a solution containing ammoniummetavanadate and ammonium heptamolybdate dissolved in hot water. Silicasol and alumina sol were added to this and the slurry was evaporated todryness over a hot plate. The dry material was heat treated at 290° C./3hours, 425° C./3 hours, and 610° C./3 hours. The composition of thecatalyst was 50% BiV₀.7 Mo₀.5 CrO_(x) +25% SiO₂ +25% Al₂ O₃.

EXAMPLE 6

Ammonium metavanadate was dissolved in hot water and ammoniumheptamolybdate was added, followed by SnO₂ sol. In a separate beaker,bismuth nitrate was dissolved in 10% nitric acid, and then chromiumnitrate was added. This solution was added slowly to the V-Mo-Sndispersion with stirring, Silica sol and then alumina sol were added tothe resulting slurry. It was stirred and heated to remove excess H₂ O,dried overnight at about 120° C., heated 3 hours at 290° C., 3 hours at425° C., ground and screened to 20-35 mesh. A portion was then calcinedat 610° C. for 3 hours. The composition was 50% BiV₀.7 MoCr₀.5 Sn₀.5O_(x) +25% SiO₂ +25% Al₂ O₃.

EXAMPLE 7

Bismuth nitrate dissolved in dilute nitric acid was mixed with asolution containing ammonium metavanadate and ammonium heptamolybdatedissolved in hot water. Silica sol and alumina sol were added to thisand the slurry was evaporated to near dryness over a hot plate. The drymaterial was heat treated at 290° C. /3 hours, 425° C./3 hours, groundand screened to 20-35 mesh and heated at 610° C./3 hours. Thecomposition of the catalyst was 50% BiV₀.7 MoO_(x) +25% SiO₂ +25% Al₂O₃.

EXAMPLE 8

This catalyst with the composition 50% BiV₀.7 Mo₀.5 W₀.5 O_(x) +25% SiO₂+25% Al₂ O₃ was prepared as described in Example 1, except that ammoniummetatungstate was included in the second solution.

EXAMPLE 9

A solution containing bismuth nitrate dissolved in dilute nitric acidwas mixed slowly with stirring with a solution containing ammoniummetavanadate, ammonium heptamolybdate and ammonium metatungstatedissolved in hot water. Silica sol and alumina sol were added to thisand the slurry was evaporated to near dryness over a hot plate, anddried overnight at 120° C. The dry material was heat treated at 290°C./3 hours, 425° C./3 hours, ground and screened to 20-35 mesh andcalcined at 610° C./3 hours. The composition of the catalyst was 50%BiV₀.7 Mo₀.3 W₀.5 O_(x) +25% SiO₂ +25% Al₂ O₃.

EXAMPLE 10

A catalyst having the empirical composition 50 wt % Bi₄ Ce₄ Mo₁₀ W₂O_(x) +50 wt % SiO₂ was made as follows:

1765.65 g of (NH₄)₆ Mo₇ O₂₄.4 H₂ O were dissolved in 2000 ml warm water.545.7 g (NH₄)₆ H₂ W₁₂ O₄₀ . H₂ O--85% WO₃ --were dissolved with theaddition of more H₂ O, to make a solution of 4750 ml. A 40 wt % SiO₂ sol(NH₄ ⁺ stabilized) was added in the amount of 8728.75 g.

In a separate beaker, 1940.4 g Bi(NO₃)₃. 5 H₂ O were dissolved in amixture of 47.5 ml conc. HNO₃ and 250 ml H₂ O. 2193.04 g (NH₄)₂ Ce(NO₃)₆were then dissolved in the solution. The resulting solution was addedslowly with stirring to the molybdate tungstate silica solution. The pHof the resulting slurry was adjusted to about 3 by the addition of about1500 ml of concentrated ammonium hydroxide. A portion of this slurry wasthen heated and stirred to remove excess water. It was dried overnightat 110° C.

The dried material was denitrified by heating at 290° C. or 3 hours andthen at 425° C. for 3 hours. It was ground and screened to between 20-35mesh particle size. Final calcination was at 650° C. for 3 hours.

In the ammoxidation runs of the following examples summarized in Table1, the mixture of catalysts is in a tubular 3/8 inch I.D. stainlesssteel fixed bed reactor. To make the mixture of particulate catalysts,the desired weight of each of the two catalyst compositions is put in avial and shaken until uniformly dispersed before placing the desiredamount of the catalyst mixture in the reaction tube. The reactor isequipped with a preheat leg and is immersed in a temperature controlledmolten salt bath. The gaseous feed components are metered through massflow controllers into the bottom of the reactor through the preheat leg.Water is introduced through a septum at the top of the preheat leg,using a syringe pump. The feed is fed to the catalyst for a pre-run of 1hour before collection of product unless a longer pre-run time is noted;the runs of each example last 30-60 minutes during which the product iscollected for analysis.

EXAMPLE 11

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 1 and the catalystof Example 10 in the weight ratio of the former to the latter of 1.0.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.4seconds. Analysis of the reactor effluent showed that propane conversionwas 12.2 percent; yield and selectivity of propane to acrylonitrile were6.3 and 51.6 percent, respectively.

EXAMPLE 12

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 2 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.36.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 2.0seconds. Analysis of the reactor effluent showed that propane conversionwas 11.6 percent; yield and selectivity of propane to acrylonitrile were6.6 and 56.9 percent, respectively.

EXAMPLE 13

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 4 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.11.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.7seconds. Analysis of the reactor effluent showed that propane conversionwas 11.8 percent; yield and selectivity of propane to acrylonitrile were6.4 and 54.1 percent, respectively.

EXAMPLE 14

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 3 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.15.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.8seconds. Analysis of the reactor effluent showed that propane conversionwas 10.6 percent; yield and selectivity of propane to acrylonitrile were6.1 and 57.3 percent, respectively.

EXAMPLE 15

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 5 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.15.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ 1H₂ O. The contact time was 1.8seconds. Analysis of the reactor effluent showed that propane conversionwas 12.3 percent; yield and selectivity of propane to acrylonitrile wereand 7.3 and 58.9 percent, respectively.

EXAMPLE 16

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 6 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.11.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.5seconds. Analysis of the reactor effluent showed that propane conversionwas 11.6 percent; yield and selectivity of propane to acrylonitrile were6.5 and 56.2 percent, respectively.

EXAMPLE 17

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 9 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.15.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.8seconds. Analysis of the reactor effluent showed that propane conversionwas 7.8 percent; yield and selectivity of propane to acrylonitrile were4.6 and 58.8 percent, respectively.

EXAMPLE 18

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 8 and the catalystof Example 10 in the weight ratio of the former to the latter of 0.45.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 2.1seconds. Analysis of the reactor effluent showed that propane conversionwas 11.7 percent; yield and selectivity of propane to acrylonitrile were7.0 and 60.0 percent, respectively.

EXAMPLE 19

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 7 and the catalystof Example 10 in the weight ratio of the former to the latter of 1.0.Water was introduced through a septum at the top of the preheat leg,using a syringe pump. The reaction temperature was 470° C. and the molarfeed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was 1.4seconds. Analysis of the reactor effluent showed that propane conversionwas 11.6 percent; yield and selectivity of propane to acrylonitrile were5.9 and 50.9 percent, respectively.

EXAMPLE 20

This catalyst with the composition 50% BiV₀.7 W₀.5 O_(x) +25% SiO₂ +25%Al₂ O₃ was prepared as described in Example 1, except that ammoniummetatungstate was used instead of ammonium heptamolybdate.

EXAMPLE 21

In this example the gaseous feed components were metered through massflow controllers into the bottom of the reactor through the preheat leg.The catalyst was a mixture of the catalyst of Example 20 and thecatalyst of Example 10 in the weight ratio of the former to the latterof 0.15. Water was introduced through a septum at the top of the preheatleg, using a syringe pump. The reaction temperature was 470° C. and themolar feed ratios were 5 propane/1NH₃ /2O₂ /1H₂ O. The contact time was1.9 seconds. Analysis of the reactor effluent showed that propaneconversion was 7.4 percent; yield and selectivity of propane toacrylonitrile were 4.1 and 54.8 percent, respectively.

As will be evident to those skilled in the art various modifications ofthis invention can be made or followed in the light of the foregoingdisclosure and discussion without departing from the spirit and scope ofthe disclosure or from the scope of the claims.

We claim:
 1. A process for the ammoxidation of a C₃ to C₅ paraffin to anα,β-unsaturated mononitrile which comprises contacting in a reactionzone said paraffin in the vapor phase in admixture with ammonia,molecular oxygen, and optionally an inert gaseous diluent, with anintimate particulate mixture of a first catalyst composition and asecond catalyst composition, said feed to the reaction zone containing amole ratio of paraffin:NH₃ in the range from 2 to 16, and a mole ratioof paraffin:O₂ in the range from 1 to 10 said first catalyst compositionbeing 0-99 weight percent of a diluent/support and 100-1 weight percentof a catalyst having oxygen and the cation components in the proportionsindicated by the empirical formula:

    Bi.sub.a V.sub.b L.sub.l M.sub.m T.sub.t O.sub.x,          formula (1)

wherein L is one or more of K, Cs, Rb and Tl; M is one or more of Mo, W,Cr, Ge, Sb, Sn, P, Pb and B; T is one or more of Zn, Nb, Ta, Fe, Co, NiCu, Mn, Ti and rare earths, a=1-25 b=1-50 l=0-1 m=0.1-20 t=0-20 x isdetermined by the oxidation state of the other elements in the catalyst,(a+b):(l+m+t)=20:1 to 1:5 a:b=1:5-5:1with the proviso that the atomicratio of Mo:V is zero to <10; said second catalyst composition being0-99 weight percent of a diluent/support and 100-1 weight percent of acatalyst having oxygen and the cation components in the proportionsindicated by the empirical formula:

    Bi.sub.n Ce.sub.p D.sub.d E.sub.e F.sub.f Mo.sub.12 W.sub.g V.sub.v O.sub.yformula ( 2)

where D is one or more of Fe, Mn, Pb, Co, Ni, Cu, Sn, P, Cr, Y, Mg, Ca,Sr, Ba and rare earths other than Ce and Sm; E is one or more of Sb, Ge,As, Se, and Te; F is one or more of an alkali metal, Tl, Ag and Sm andwhere n is 0.01-24, p is 0.01-24; (n+p) is 0.1-24, d is 0-10, e is 0-10,f is 0-6, g is 0-8, v is 0-0.5 and y is determined by the oxidationstate of the other elements present, wherein the weight ratio in saidmixture of said first catalyst composition to said second catalystcomposition is in the range of 0.001 to 2.5.
 2. A process of claim 1wherein said mole ratio of paraffin:NH₃ is in the range from 3 to
 7. 3.A process of claim 1 wherein said mole ratio of paraffins:O₂ is in therange from 1.5 to
 5. 4. A process of claim 2 wherein said mole ratio ofparaffin:O₂ is in the range from 1.5 to
 5. 5. A process according toclaim 1 wherein the mole ratio of O₂ to NH₃ in the feed to the reactionzone is in the range from 1 to
 10. 6. A process according to claim 1wherein the mole ratio of inert gaseous diluent to paraffin in the feedto the reaction zone is in the range from zero to
 5. 7. A process ofclaim 1 wherein said paraffin is propane or isobutane.
 8. A process ofclaim 1 wherein said paraffin is propane.
 9. A process of claim 2wherein said paraffin is propane or isobutane.
 10. A process of claim 4wherein said paraffin is propane.